The standard design of the drive train consists in positioning the gearbox and the electrical generator behind the wind turbine rotor and within the nacelle. This is the most compact configuration. Within this configuration, the rotor rotation shaft design and its integration with the drive train is one of the most fundamental points in the mechanical design of a wind turbine.
Normally, the joint between the rotor rotation shaft and the gearbox is made at the plant and, once assembled, it is mounted inside the nacelle and then transported to the site for installation.
The rotor rotation shaft is mounted on separate bearings and is joined to the gearbox rotation shaft by a friction-type (choke) or bolted joint. This joint in certain machines employs a collar mounted on the outside of the union forming the rotor shaft and the gearbox shaft. The rotor shaft is inserted into the hole in the gearbox shaft. The hydraulic (or mechanical) collar compresses the hollow shaft with the rotor shaft and transmits the moments of torsion by friction.
For machines with an integrated compact train, the joint is bolted and an additive is employed to have a more effective friction surface, as indicated in European patent EP2075466.
Nonetheless, these types of joints could result in the following problems:
The bolted joint and the additives used in the joint for machines with an integrated compact train show little modularity and its maintenance requires maneuvering room in the nacelle. The joint made with a collar demands a delicate adjustment during the axial movement of the elements, not to mention the elevated prices of the materials constituting the collar.
Bolted joints in the field use a combination of bolts and pins to secure flanges smaller than the ones corresponding to transmit solely torsion by friction. This is done to keep from penalizing the size of the gearbox shaft bearing, of the shaft itself, and of the flange. Nevertheless, friction-type joints are more versatile for assembly and disassembly and distribute work and tensions better.
Drive train assembly and subsequent upkeep/maintenance is highly substantial and directly affects the costs of wind turbines. The rotor shaft transfers large amounts of stress and its joint with the gearbox shaft must be calculated in great detail. These elements are rotating shafts and are often covered with their corresponding covers. Their interchangeability and accessibility must be kept in mind.